The mainmessage here is "We’ve identified a shift in OS 10.10 behavior that seems to be tripping us up and are testing a fix to roll into our next release. Unfortunately the only workaround until then is to downgrade to the previous version of Lightroom. Thanks to all of you who provided details to help us track this down"

Try hovering with your mouse/pointer over the Name Plate (see image above) until the icon for the pull-down menu shows up. Click on it, to see the activity window and then ensure that LR Mobile is not paused.